1. Field of the Invention
The present invention relates, generally to a method of determining an equivalent value for a failed sensor and, more specifically, to a method of determining an equivalent sensor output value for an inoperative sensor employed in an array within a vehicle seat having an occupancy sensing system.
2. Description of the Related Art
Automotive vehicles employ seating systems that accommodate the passengers of the vehicle. The seating systems include restraint systems that are calculated to restrain and protect the occupants in the event of a collision. The primary restraint system commonly employed in most vehicles today is the seatbelt. Seatbelts usually include a lap belt and a shoulder belt that extends diagonally across the occupant's torso from one end of the lap belt to a mounting structure located proximate to the occupant's opposite shoulder.
In addition, automotive vehicles may include supplemental restraint systems. The most common supplemental restraint system employed in automotive vehicles today is the inflatable airbag. In the event of a collision, the airbags are deployed as an additional means of restraining and protecting the occupants of the vehicle. Originally, the supplemental inflatable restraints (airbags) were deployed in the event of a collision whether or not any given seat was occupied. These supplemental inflatable restraints and their associated deployment systems are expensive and over time this deployment strategy was deemed not to be cost effective. Thus, there became a recognized need in the art for a means to selectively control the deployment of the airbags such that deployment occurs only when the seat is occupied.
Partially in response to this need, vehicle safety systems have been proposed that include vehicle occupant sensing systems capable of detecting whether or not a given seat is occupied. The systems act as a switch in controlling the deployment of a corresponding air bag. As such, if the occupant sensing device detects that a seat is unoccupied during a collision, it can prevent the corresponding air bag from deploying, thereby saving the vehicle owner the unnecessary cost of replacing the expended air bag.
Furthermore, many airbag deployment forces and speeds have generally been optimized to restrain one hundred eighty pound males because the one hundred eighty pound male represents the mean average for all types of vehicle occupants. However, the airbag deployment force and speed required to restrain a one hundred eighty pound male exceeds that which are required to restrain smaller occupants, such as some females and small children. Thus, there became a recognized need in the art for occupant sensing systems that could be used to selectively control the deployment of the airbags when a person below a predetermined weight occupies the seat.
Accordingly, other vehicle safety systems have been proposed that are capable of detecting the weight of an occupant. In one such air bag system, if the occupant's weight falls below a predetermined level, then the system can suppress the inflation of the air bag or will prevent the air bag from deploying at all. This reduces the risk of injury that the inflating air bag could otherwise cause to the smaller-sized occupant.
Also, many airbag deployment forces and speeds have generally been optimized to restrain a person sitting generally upright towards the back of the seat. However, the airbag deployment force and speed may inappropriately restrain a person sitting otherwise. Thus, there became a recognized need in the art for a way to selectively control the deployment of an airbag depending on the occupant's sitting position.
Partially in response to this need, other vehicle safety systems have been proposed that are capable of detecting the position of an occupant within a seat. For example, if the system detects that the occupant is positioned toward the front of the seat, the system will suppress the inflation of the air bag or will prevent the air bag from deploying at all. This reduces the risk of injury that the inflating air bag could otherwise cause to the occupant. It can be appreciated that these occupant sensing systems provide valuable data, allowing the vehicle safety systems to function more effectively to reduce injuries to vehicle occupants.
One necessary component of each of the known systems discussed above includes some means for sensing the presence of the vehicle occupant in the seat. One such means may include a sensor device supported within the lower seat cushion of the vehicle seat. For example, U.S. published patent application having U.S. Ser. No. 10/249,527 and Publication No. U.S. 2003/0196495 A1 filed in the name of Saunders et al. discloses a method and apparatus for sensing seat occupancy including a sensor/emitter pair that is supported within a preassembled one-piece cylinder-shaped housing. The housing is adapted to be mounted within a hole formed in the seat cushion and extending from the B-surface toward the A-surface of the seat cushion. The sensor/emitter pair supported in the housing includes an emitter that is mounted within the seat cushion and spaced below the upper or A-surface of the seat cushion. In addition, the sensor is also supported by the housing within the seat cushion but spaced below the emitter. The cylindrical housing is formed of a compressible, rubber-like material that is responsive to loads placed on the upper surface of the seat cushion. The housing compresses in response to a load on the seat cushion. The load is detected through movement of the emitter toward the sensor as the housing is compressed. The housing is sufficiently resilient to restore the emitter to full height when no load is applied to the upper surface of the seat cushion. The Saunders et al. system also includes a processor for receiving the sensor signals and interpreting the signals to produce an output to indicate the presence of an occupant in the seat.
The sensors are arranged into a grid, or an array so that the sensors are collectively used to provide the raw input data as a depression or deflection pattern in the seat cushion. In this manner, systems of the type known in the related art take the data from the sensor array and process it, by a number of different means, in an attempt to determine the physical presence in the seat. A number of the prior art systems sense the deflection of portions of the vehicle seat and attempt to discern from the sensor array data a recognized pattern that corresponds to one of the specified occupant classifications. To accomplish the pattern recognition, the best of these newer systems take the data derived from the sensed seat occupancy and process it through an artificial neural network. Artificial neural networks are more commonly referred to as neural networks, or simply, neural nets (NN).
In general terms, a NN is essentially an interconnected assembly of simple processing element units, or nodes. The processing ability of the network is stored in the inter-unit connection strengths, or weights, obtained by a process of adaptation to, or learning from, a set of training patterns. The NN may simply have an input and an output layer of units, or have an additional “hidden” layer or layers of units that internally direct the interconnection processes. The benefit to employing a NN approach is that, if properly trained, the NN will be able to generalize and infer the correct output responses from limited input data. Specifically in the case at hand, the NN based occupancy sensing systems determine that a physical presence is in a vehicle seat, recognize the type of physical presence by the sensor pattern it presents and pass this information to a restraint system control to determine if the pattern classification requires deployment or suppression of the airbag or other restraints.
In this regard, NNs applied to vehicle occupancy sensing systems, especially those that employ supervised learning such as discussed in the co-pending application U.S. Ser. No. 10/748,504, entitled Method of Occupancy Classification in a Vehicle Seat filed Dec. 30, 2003 have proven to be successful. However, from a physical standpoint, all occupancy sensing systems employing sensors that deflect or are moved in response to a physical presence in the seat fundamentally rely on receiving accurate and reliable data from the sensors to operate properly.
As mentioned above, various styles and types of sensors have been employed in occupancy sensing systems, with the Hall-effect sensor type being the most common. Regardless of the type of sensor employed, physical failure of at least one of the sensors in the array during the life of the seat is, at the least, a possibility. Even with robust sensors constructed to withstand millions of deflections or compressions, other factors such as foreign object interference, loss of connection to the array, or physical damage to the seat are possible interfering or damaging effects that will prevent valid sensor data from reaching the NN.
Prior art occupancy sensing systems rely on the fact that vehicle seat employs a sensor array for occupant classification and that the sensors function as a cohesive group rather than as independent entities. In other words, conventional occupancy classification systems trust that since the seat foam and seat covering cause the sensors to generally deflect as a group that the output of the array as a group continues to present valid data even after the failure of one of the sensors. However, even though there is some cooperative influence upon the array of sensors as a whole, the loss of even one sensor can cause erroneous occupancy classifications to occur. This is particularly true in light of the ever-tightening Federal Safety Standards that continue to require more accurate discernment between the occupancy classification groups. Of particular concern, if an occupancy classification is erroneously determined by relying on the sensor array that has a failed sensor, serious problems may arise by allowing for improper suppression or deployment of the restraint systems with respect to the actual occupant. Furthermore, current occupancy sensing and classification systems are unable to identify a sensor that is not functioning properly and therefore lack the means to compensate for the failed sensor. Thus, not only will the failed sensor continue to cause erroneous occupancy classifications to be determined for each respective occupant, but the erroneous determinations will go unnoticed allowing an improper deployment action in the restraint system to ultimately occur.
Accordingly, there remains a need in the art for a method of determining when a sensor in the array of an occupancy sensing system has failed. Furthermore, there remains a need in the art for a method that can determined an equivalent output value for the failed sensor of an occupancy sensing system and use that value as a replacement for the failed sensor until the occupancy sensing system can be repaired.